The purpose of the proposed studies is to understand the HIV-1 frameshift (FS) mechanism and to learn how it can be targeted with small, drug-like molecules. The HIV-1 FS site is a highly conserved genomic RNA structure located between the gag and pol reading frames. Its purpose is to stimulate a -1 FS that is required for expression of the Pol genes, which are in the -1 reading frame relative to Gag. We have solved the structure of the HIV-1 FS RNA, both alone and in complex with small drug-like molecules. We will use high throughput screens to identify small molecules that bind to and modulate the HIV-1 FS RNA, both in vitro and in vivo. The best small molecule ligands will be identified as lead compounds. The structures of the HIV-1 FS RNA in complex with lead compounds will be solved, in order to understand the basis for their modes of action. From this information, novel second generation compounds will be developed with improved affinity, specificity and potency. Additionally, we will investigate the FS mechanism, which is currently not well understood. Elucidation of the FS mechanism will provide a better understanding of this essential feature of the viral life cycle, which is utilized by all retroviruses. Finally, we will investigate the structure and function of the entire HIV-1 genomic FS domain, which has been recently identified and is hypothesized to function in slowing the kinetics of translation prior to the FS.